Patent Document 1 discloses a pressure sensor of related art that detects a pressure based on a deformation amount of a diaphragm. The pressure sensor according to Patent Document 1 is structured so that a silicon substrate having a diaphragm functioning as a movable electrode is joined with a glass substrate so that one surface of the diaphragm is sealed to provide a pressure reference room.
The diaphragm deflects in accordance with a difference between, under a usage environment, an external pressure and a reference pressure in the pressure reference room to have a contact with a dielectric material layer on a glass substrate. Under the dielectric material layer of the glass substrate, opposed electrodes are formed. In this manner, a change of the contact area depending on an external pressure is detected as a change in the interelectrode capacity, thereby providing a function of a pressure sensor. The pressure sensor having the structure as described above is called as a touch mode capacitive pressure sensor and has a high detection sensitivity and a high pressure resistance.
Patent Document 1JP-A-2002-214058
In the above-described pressure sensor, a silicon substrate can be joined with a glass substrate by an anodic bonding. This anodic bonding does not involve gas generation in contrast with a junction using jointing material (e.g., brazing material) and thus is suitable for accurately setting a reference pressure in the pressure reference room. This anodic bonding is also a method that is suitable for accurately specifying a gap between a movable electrode and opposed electrodes (dielectric material layer).
However, this anodic bonding requires the substrates to be heated. This causes, when to-be-joined substrates have different thermal expansion coefficients, a problem of an in-plane distortion in the substrates. The diaphragm in particular tends to deform and thus is easily influenced by such a distortion, which may cause fluctuation in the characteristics.